Enzootic bovine leukemia (EBL) is an infectious disease of cattle caused by a type C retrovirus, BLV (Bovine Leukemia Virus) and consists of lymphatic node hypertrophy. The disease is characterized by a long incubation period (up to 7 years) and, in most cases, (ca. 60%) proceeds without symptoms. Lymphatic cysts form in a portion of adult cattle (10-30%), whereas 1-10% develop lymphatic sarcomas on various internal organs, with a marked increase of B lymphocytes.
A strong immune response occurs in infected individuals, which is used in serological diagnostics. Despite the fact that the titer of anti-BLV antibodies increases as the disease progresses, they are not able to halt the infection. Because the disease develops asymptomatically through a long initial phase, the only effective method of preventing transmission are frequent serological diagnostics and the elimination of infected animals. Serological assays are performed on animals over 6 months, when maternal antibodies have begun disappearing. The virus itself can be detected in isolated peripheral lymphocytes using an electron microscope, and viral DNA can be diagnosed using PCR. Immunological assays are used most frequently to diagnose bovine leukemia: gel immunodiffusion (ACID), immunoenzymatic assays (ELISA) as well as radioimmunological detection. These methods make use of antibodies against the antigenic proteins gp51 and p24.